An experimental technique has been developed to study the deposition of colloidal particles under well controlled hydrodynamic conditions. The deposition process is observed under a microscope and recorded on video tape for further analysis. Fluid flow conditions in the experimental set-up were determined by numerical solution of the Navier-Stokes equations. Mass transfer equations were solved numerically (taking into account hydrodynamic, gravitational, electric double layer, and dispersion forces) for the stagnation point region. Also, some analytical solutions are presented. Deposition has been studied of 0.5/~m polystyrene latex particles on cover glass slides used as collectors. From an analysis of the shape of the coating density vs. time curves and independently from the distribution of the particles on collector surfaces, it was found that one particle is able to block an area of about 20 to 30 times its geometrical cross-section. The initial flux of particles to the collector for a given salt concentration yeas found to depend strongly on the method of cleaning the collector surface. In general the flux and the escape of particles to and from the collector surface are sensitive to the interaction energy at small separations. The direct method of observing particle deposition and detachnlent could lead to important insights into the nature of particle-wall interactions at near contact.

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HIGHLIGHTS • The most common chemical treatments of cellulose to synthesize nanostructured cellulose are highlighted. • Various surface modifications of cellulose to develop non-leaching and durable antibacterial materials are discussed. • Biocompatibility and antibacterial performance of non-leaching surface-modified cellulosic materials along with their current challenges are discussed.

Block copolymers can form a broad range of self-assembled aggregates. In solution, planar assemblies usually form closed structures such as vesicles; thus, free-standing sheet formation can be challenging. While most polymer single crystals are planar, their growth usually occurs by uptake of individual chains. Here we report a novel lamella formation mechanism: core-crystalline spherical micelles link up to form rods in solution, which then associate to yield planar arrays. For the system of poly(ethylene oxide)-block-polycaprolactone in water, co-assembly with homopolycaprolactone can induce a series of morphological changes that yield either rods or lamellae. The underlying lamella formation mechanism was elucidated by electron microscopy, while light scattering was used to probe the kinetics. The hierarchical growth of lamellae from one-dimensional rod subunits, which had been formed from spherical assemblies, is novel and controllable in terms of product size and aspect ratio.

Electrosterically stabilized nanocrystalline cellulose (ENCC) was modified in three ways: (1) the hydroxyl groups on C2 and C3 of glucose repeat units of ENCC were converted to aldehyde groups by periodate oxidation to various extents; (2) the carboxyl groups in the sodium form on ENCC were converted to the acid form by treating them with an acid-type ion-exchange resin; and (3) ENCC was cross-linked in two different ways by employing adipic dihydrazide as a cross-linker and water-soluble 1-ethyl-3-[3-(dimethylaminopropyl)] carbodiimide as a carboxyl-activating agent. Films were prepared from these modified ENCC suspensions by vacuum filtration. The effects of these three modifications on the properties of films were investigated by a variety of techniques, including UV-visible spectroscopy, a tensile test, thermogravimetric analysis (TGA), the water vapor transmission rate (WVTR), and contact angle (CA) studies. On the basis of the results from UV spectra, the transmittance of these films was as high as 87%, which shows them to be highly transparent. The tensile strength of these films was increased with increasing aldehyde content. From TGA and WVTR experiments, cross-linked films showed much higher thermal stability and lower water permeability. Furthermore, although the original cellulose is hydrophilic, these films also exhibited a certain hydrophobic behavior. Films treated by trichloromethylsilane become superhydrophobic. The unique characteristics of these transparent films are very promising for potential applications in flexible packaging and other high-technology products.

Dilute aqueous solutions of broad and narrow distribution poly(ethylene oxide) fractions were studied using dynamic (DLS) and static (SLS) light scattering, as well as gel permeation chromatography (GPC). It was found that above a critical self-association concentration, which depends on the molecular weight of the PEO, polymer clusters and free polymer coils coexist in a thermodynamic equilibrium. The polymer clusters can be removed by filtration and begin to reform spontaneously in solution within 30 min after filtration. A steady-state amount of PEO in clusters is attained within about 24 h. At steady-state the narrow-distribution and broad-distribution PEO samples have 7−10% wt/wt and 12−18% wt/wt of the polymer present as clusters in solution, respectively, at PEO concentrations of about 250 mg/L. It was found that the PEO clusters were composed of a few hundred polymer chains per cluster. From DLS the polymer cluster diameters were found to be independent of molecular weight and to decrease, with time, from 0.90 to 0.45 μm. In dynamic light scattering studies of the PEO solutions containing clusters, the light scattered from the clusters is mixed with light scattered from freely dissolved molecules. This mixing of light with different Doppler-shifted frequencies leads to quasi-heterodyning.

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